The present invention relates in general to instruments for acquiring, storing and displaying data representing input signals, and in particular to an instrument permitting a user to erase such data easily when stored in memory.
A typical digital storage oscilloscope includes an acquisition system for generating waveform data sequences representing magnitudes of successive samples of input signals. The oscilloscope further includes a memory for storing acquired data sequences and a system for generating waveform displays on a cathode ray tube (CRT) screen depicting the stored waveform data. The oscilloscope may also store and display additional data regarding each displayed waveform such as range settings and sampling rates. Such oscilloscopes may use non-volatile memory for storing waveform data sequences and other data so that the data is retained when the oscilloscope is turned off or unplugged. "Non-volatile" memory is defined herein as read and write accessible memory that retains its data when the system that read and write accesses that memory loses its power source, while volatile memory is one that loses its contents when the system that accesses it loses its power. Oscilloscopes typically use battery driven non-volatile memory although other varieties of non-volatile memory may be employed.
When information stored in an oscilloscope involves valuable trade secret data, the storage oscilloscope represents a security problem, particularly when the oscilloscope uses non-volatile memory for storing the data. To prevent others from accessing sensitive data in an oscilloscope, a user may wish to erase the data from the oscilloscope memory before leaving the oscilloscope unattended, allowing another person to use it, or removing it from a secure work site. Digital storage oscilloscopes of the prior art, employing volatile or non-volatile memory can "erase" waveform data sequences and other data stored in the memory by writing over that data with newly acquired data. Furthermore, to "erase" important waveform data stored in an oscilloscope using only volatile memory, a user can simply turn the oscilloscope off. However, when the oscilloscope employs non-volatile memory, a user can only erase important data therein by using the oscilloscope in such a way that this data is written over. Such a procedure is time-consuming and difficult to perform, particularly by security personnel not familiar with oscilloscope operation. In addition, there can be areas of memory storing sensitive information that are inaccessible to the user when operating the oscilloscope in a normal fashion.
Similar security problems occur with instruments such as spectrum and logic analyzers that generate and store data representing various observed phenomena